The present invention relates to a method of stacking packs of printed circuit boards; to a pack loading and unloading device and pack unpinning mechanism for a machine tool; and to a pack of printed circuit boards stackable using the method according to the invention.
As is known, for machining on a machine tool, packs of printed circuit boards are normally provided with two locating pins along the center line and adjacent to two opposite edges of the pack, which pins project from one face of the pack and are essential for aligning and securing the pack to the table of the machine tool.
The pins, however, prevent the packs from being stacked contacting one another, e.g. for storage, and, to prevent the pins of one pack from damaging the adjacent pack, the packs must be separated by a distance greater than the length of the pins. For this reason, the packs are normally stacked in special trays for protecting the pins and maintaining the necessary distance between the packs. Such trays, however, take up an enormous amount of space, thus increasing the storage cost of the packs.
Moreover, the pins seriously complicate loading and unloading of the packs on and off the machine tool. One known machine with a number of machining heads comprises an automatic pack loading and unloading device, wherein two mechanisms are provided on either side of the machine for vertically moving two racks, one for loading and the other for unloading packs of printed circuit boards.
By means of push actuators associated with each machining head, the packs are moved along the X axis on two guides parallel to the X axis, and which are movable vertically to keep the pins detached from the table during transport; and the packs are then fed in steps to the various machining heads. As a result, the loading and unloading device is extremely complicated, expensive and slow-operating.
Another known machine provides for feeding the machining head by means of a rack having a number of pack supporting trays. The rack is located at the rear of the machine, and the pack is pushed along the Y axis of the tray onto a pack aligning and clamping fixture having a groove for housing the pins.
At each loading and unloading cycle, the device must transfer the machined pack back onto the original tray and remove another pack from the next tray. Moreover, in the case of a number of machining heads, an equal number of racks are required, which means this device, too, is fairly complicated and expensive.